This invention relates to a multilayer printed wiring board used as a package board for mounting an IC chip or the like and a process of producing the same, and more particularly to a multilayer printed wiring board capable of providing a high density wiring easily and of preventing the formation of cracks or the like in through-holes or in the neighborhood thereof when heat cycle occurs, for example.
This invention also relates to a resist composition for filling through-hole of a multilayer printed wiring board, which is used for ensuring satisfactory electric connections between viaholes and through-holes even at high temperature and high humidity conditions or under such conditions as to cause heat cycle.
In general, through-holes are formed for electrically connecting the front surface to the back surface of a core substrate (hereinafter simply referred to as xe2x80x9csubstratexe2x80x9d) of a both-sided multilayer printed wiring board. These through-holes are, however, considered as dead spaces in designing of a circuit, and hence become one of the factors which prevent wiring from densifying.
For reducing such dead spaces, there have been disclosed, for example, following technologies;
{circle around (1)} Japanese Unexamined Patent Publication No. 9-8424 discloses a technique of filling though-holes with a resin and roughening the resin on its surface and forming a mount pad on the roughened surface.
{circle around (2)} Japanese Unexamined Patent Publication No. 2-196494 discloses a technique of filling through-holes with a conductive paste, and dissolving and removing an electrolytic plated film covering through-holes to form landless though-holes.
{circle around (3)} Japanese Unexamined Patent Publication No. 1-143292 discloses a technique of filling though-holes with a conductive paste and subjecting the resultant substrate to a copper plating to form a plated film covering the paste.
{circle around (4)} Japanese Unexamined Patent Publication No. 4-92496 discloses a technique of forming, for example, a copper plated film onto all over the surface of a substrate inclusive of internal surfaces of through-holes by electroless plating, filling the inside of the though-holes with an electrically conductive material (conductive paste) and then covering the substrate with a copper plated film so as to encapsulate the electrically conductive material in the through-holes.
The conventional techniques mentioned above, however, have the following disadvantages.
{circle around (1)} Such a both-sided multilayer printed wiring board as is described in Japanese Unexamined Patent Publication No. 9-8424 requires a roughening treatment of the surface of a resin in order to ensure adhesion between the resin filled in through-holes and the mount pad. In addition, since coefficients of thermal expansion between a resin and a metal are different, the conductor layer on the through-holes may peel or form cracks due to heat cycle.
{circle around (2)} According to the technique described in Japanese Unexamined Patent Publication No. 2-196494, when openings for viaholes are formed just above the through-holes of an interlaminar resin layer by laser beam, the conductive paste is exposed to the openings and thereby a resin ingredient in the conductive paste is also eroded.
{circle around (3)} In such a printed wiring board as is described in Japanese Unexamined Patent Publication No. 1-143292, the conductive paste is in direct contact with the internal surfaces of through-holes of a resin substrate so that metal ions are apt to disperse from the surfaces to the inside of the substrate when it takes up moisture. The dispersion (migration) of metal ions causes development of a short circuit between the conductor layer and the through-holes.
{circle around (4)} In such a printed wiring board as is described in Japanese Unexamined Patent Publication No. 4-92496, gaps or voids are tend to form because of a poor adhesion between the conductor layer and the electric conductive material in the through-holes. The formation of voids between the electric conductive material and a through-hole invites delamination of the conductor layer or generation of cracks on the through-hole in the use at high temperature and high humidity conditions due to air or water accumulated in the voids.
Incidentally, there may be some demands to connect a through-hole to a viahole formed on a substrate. In this case, connection is generally made by forming a pad called as land protruding on the periphery of the through-hole and connecting the through-hole to viahole through the interposition of the pad. The pad is, however, frequently obstructive because it is formed protruding on the outer periphery of the through-hole and hence causes, for example, an increasing pitch between adjacent through-holes each other. This becomes an impediment to achieve a high density wiring or to narrower intervals between through-holes.
On the contrary, as examples conventional multilayer wiring boards having a high density wiring function, Japanese Unexamined Patent Publication No. 6-275959 discloses a multilayer printed wiring board obtained by filling through-holes with a filler, forming a conductor layer thereonto, and forming viaholes on the conductor layer, and Japanese Unexamined Patent Publication No. 5-243728 discloses a process of filling through-holes with a conductive paste and curing the paste, polishing a substrate on its surface and then forming a conductor layer covering the through-holes, and mounting a surface mount part on the conductor layer.
According to these conventional techniques, a surface mount part can be connected to through-holes so as to provide high density wiring or through-holes, but they have the following disadvantages.
{circle around (5)} The multilayer printed wiring board as practically exemplified in Japanese Unexamined Patent Publication No. 6-275959 is obtained by filling through-holes with a photosensitive resin as the filler. In such a wiring board, delamination between the filler and the conductor layer occurs when exposed to high temperature and high humidity conditions such as in Pressure Cooker Test, and a connection reliability between viaholes formed on the conductor layer and through-holes cannot be obtained.
{circle around (6)} The technique disclosed in Japanese Unexamined Patent Publication No. 5-243728 is not a technique relating to a build-up multilayer printed wiring board and hence does not make the most of the high density wiring function inherent in the build-up method.
The present invention has been accomplished to solve the aforementioned problems inherent to the conventional techniques, and it is a main object of the invention to provide a multilayer printed wiring board which can easily ensure high density wiring and a production process thereof.
It is another object of the invention to provide a construction of a multilayer printed wiring board which is effective for preventing delamination between a filler for though-hole and a conductor layer, for inhibiting delamination and formation of cracks between a conductor circuit and an interlaminar insulating resin layer, for preventing metal ions in the filler from diffusing and for protecting the filler from erosion by a laser beam.
It is still another object of the invention is to provide high density through-hole intervals and wiring in a build-up multilayer printed wiring board without reducing an electric connection reliability between through-holes and viaholes at high temperature and high humidity conditions.
It is yet another object of the invention to provide a construction of a multilayer printed wiring board for ensuring a reliable electric connection between an internal layer circuit inside a substrate and build-up multilayer circuit layers on both surfaces of the substrate even when the substrate is multilayered.
A yet further object of the invention is to provide a construction of a resin composition used for filling through-hole of the aforementioned multilayer printed wiring boards.
The present invention provides a multilayer printed wiring board being composed of a substrate provided with through-holes, and a conductor circuit formed on the substrate through the interposition of an interlaminar insulating resin layer, the through-holes being filled with a filler, wherein the internal surfaces of the through-holes are roughened, and the filler is composed of metal particles, and a thermosetting resin or a thermoplastic resin.
The invention also provides a multilayer printed wiring board being composed of a substrate provided with through-holes, and a conductor circuit formed on the substrate through the interposition of an interlaminar insulating resin layer, the through-holes being filled with a filler, wherein internal surfaces of the through-holes are roughened, and the filler is composed of metal particles and a thermosetting resin or a thermoplastic resin, and an exposed portion of the filler in the through-holes is covered with a through-hole-covering conductor layer.
In addition, the present invention provides a multilayer printed wiring board being composed of a substrate provided with through-holes, and a conductor circuit formed on the substrate through the interposition of an interlaminar insulating resin layer, the through-holes being filled with a filler, wherein internal surfaces of the through-holes are roughened, and the filler is composed of metal particles and a thermosetting resin or a thermoplastic resin, and an exposed portion of the filler in the through-holes is covered with a through-hole-covering conductor layer, and the through-hole-covering conductor layer is connected to a viahole formed just above the conductor layer.
Furthermore, the present invention provides a multilayer printed wiring board comprising a multilayer core board having conductor layers in its innerlayer, and interlaminar resin insulating layers and conductor layers alternately laminated on a substrate to form buildup wiring layer connecting the conductor layers through via-hole, and is characterized in that the multilayer core board has a resin insulating layer covering the innerlayer conductor circuits formed on the core material, via-holes are formed in the resin insulating layer so as to arrive at the innerlayer conductor circuit through the layer, and through-holes are formed in the resin insulating layer and the core material to pass therethrough and are filled with a filler, and a part of the via-holes in the buildup wiring layer is located just above the through-hole and directly connected to the through-hole.
The present invention provides, in another aspect, a process of producing a multilayer printed wiring board comprising at least the following steps {circle around (1)} to {circle around (4)}:
{circle around (1)} a step of forming a conductor layer and a through-hole on both surfaces of a substrate by electroless plating, or additionally by electroplating,
{circle around (2)} a step of forming a roughened layer on the internal surface of the through-hole,
{circle around (3)} a step of filling the through-hole provided with the roughened layer on its internal surface with a filler composed of metal particles and a thermosetting resin or a thermoplastic resin, and drying and curing the filler,
{circle around (4)} a step of forming an interlaminar insulating resin layer and then forming a conductor circuit by subjecting the substrate to an electroless plating, or additionally to an electroplating.
The invention provides, in yet another aspect, a process of producing a multilayer printed wiring board comprising at least the following steps {circle around (1)} to {circle around (5)}:
{circle around (1)} a step of forming a conductor layer and a through-hole on both surfaces of a substrate by electroless plating, or additionally by electroplating,
{circle around (2)} a step of forming a roughened layer on the internal surface of the through-hole,
{circle around (3)} a step of filling the through-hole with a filler composed of metal particles and a thermosetting resin or a thermoplastic resin, and drying and curing the filler,
{circle around (4)} a step of subjecting an exposed portion of the filler on the through-hole to an electroless plating, or additionally to an electroplating to form a through-hole-covering conductor layer, and
{circle around (5)} a step of forming an interlaminar insulating resin layer and then forming a conductor circuit by electroless plating, or additionally by electroplating.
The invention provides, in a yet further aspect, a process of producing a multilayer printed wiring board comprising at least the following steps O) to 06:
Qi a step of forming a conductor layer and a through-hole on both surfaces of a substrate by electroless plating, or additionally by electroplating, @ a step of forming a roughened layer on the internal surface of the through-hole, Hi a step of filling the through-hole provided with the roughened layer on its internal surface with a filler composed of metal particles and a thermosetting resin or a thermoplastic resin, and drying and curing the filler, a step of subjecting an exposed portion of the filler on the through-hole to an electroless plating, or additionally to an electroplating to form a through-hole-covering conductor layer, a step of forming an interlaminar insulating resin layer, and 6 a step of forming a viahole and a conductor circuit in the interlaminar insulating resin layer located just above the through-hole, and connecting the viahole to the through-hole-covering conductor layer.
In addition and advantageously, the invention provides a resin composition for filling through-holes of a printed wiring board, which comprises a particulate substance, a resin and an ultrafine inorganic powder.